1. Field of the Invention
The present invention relates to a thin film magnetic head to be used for a helical scan type magnetic recording and reproducing apparatus, particularly to a magnetoresistive magnetic head for use in a reproducing a magnetic head.
2. Description of the Related Art
FIG. 24 shows a perspective view of the rotary drum of the conventional helical scan type magnetic recording and reproducing apparatus; FIG. 25 is a plane view for describing the recording method in the helical scan type magnetic recording and reproducing apparatus; FIG. 26 is a plane view showing the construction of the composite type magnetic head; FIG. 27 is a perspective view showing the construction of the magnetic head mounted on the base board of the rotary drum; FIG. 28 is a plane view of the construction of the magnetic head mounted on the rotary drum viewed from the sliding face side of the recording medium; FIG. 29 includes an enlarged construction of the area X in FIG. 28, and shows a plane view for describing the elevation adjustment of respective MR layers of the two magnetic heads; FIG. 30 shows a plane view of the reproduction track during reproduction when respective MR layers of the two magnetic heads have different elevations one another; and FIG. 31 a plane view showing how mounting errors occur when the magnetic head is mounted on the base board.
A line of information has been recorded and reproduced by a helical scan method in the magnetic recording and reproducing apparatus such as a VCR (Video Cassette Recorder) and a recording and reproducing unit for a computer using a magnetic tape as a magnetic recording medium. A plurality of the magnetic heads have been used in the helical scan type magnetic recording and reproducing apparatus in order to improve recording density and data transfer rate, wherein two magnetic heads 70 and 80 are mounted on a rotary drum 61 at two opposed positions on the outer circumference face as shown, for example, in FIG. 24.
Signals are recorded on the magnetic tape 63 wound on the rotary drum 61, or the signals recorded on the magnetic tape 63 are reproduced using these magnetic heads 70 and 80. As shown in FIG. 25, for example, signals are recorded by a so-called guard-band-less method so that a recording track T12 is made to partially overlap an area of another track T11 where signals have been recorded by the magnetic heads 70 immediately before recording with the magnetic head 80, when the rotary drum 61 is driven to rotate to record the signals from the magnetic head 80 on the magnetic tape 63. On the other hand, respective magnetic heads 70 and 80 sequentially scan the corresponding recording tracks T11 and T12 for reproduction.
A MIG (Metal-In-Gap) type head and a lamination type head have been used for the magnetic heads 70 and 80 to be used for the helical scan type magnetic recording and reproducing apparatus.
Track width has been narrowed or the recording frequency has been increased for realizing high density recording on the magnetic recording medium in the data recording and reproducing apparatus for use in the VTR and computer. As a result, the magnetic gap is also required to be narrow in compliance with narrowing the track width.
However, it is difficult to make the MIG head small size because the magnetic gap is formed by mechanical cutting to make it impossible to meet the requirement of narrowing the track width. While a high polishing accuracy of the abutting faces is required for forming the magnetic gap meeting the requirement of narrowing the track width, the polishing accuracy for the fine magnetic gap has been hardly improved. While inductance should be also low for complying with the requirement of making the recording frequency high, on the other hand, it is impossible to lower the inductance in the MIG head and lamination type head. Furthermore, the MIG head and lamination type head also have a drawback that their reproduction outputs cannot be made to be sufficiently high when one attempts to increase the recording density.
In the magnetic recording and reproducing apparatus such as a hard disk device, on the other hand, various thin film magnetic heads have been used. Commonly used thin film magnetic heads mainly comprise an induction type magnetic head (an inductive head) and reproducing magnetic heads include a magnetoresistive magnetic head (a MR head). A composite type magnetic head formed by laminating the inductive head and the MR head has been also frequently used.
Such thin film magnetic heads as described above are advantageous in that they are suitable for mass production in one lot by using a thin film deposition process, and that they are able to meet the requirement of making the dimension fine for narrowing the magnetic gap for use in the track having a narrow width. The MR head is particularly suitable for high frequency recording since it is not dependent on the relative velocity of the magnetic recording medium to enable it to directly respond to the signal magnetic field to obtain a high reproduction output, besides its inductance is considerably lower as compared with the MIG head and lamination type head.
Accordingly, use of the thin film magnetic head described above as a magnetic head is also desirable in the helical scan type magnetic recording and reproducing apparatus.
When the composite type magnetic head is applied for the magnetic heads 70 and 80 of the helical scan type magnetic recording and reproducing apparatus, for example, the magnetic head 70 is composed of a MR head 71 and an inductive head 72 as shown in FIG. 26. The MR heads 71 is formed by sequentially laminating an insulation layer 71b, a lower shield layer 71c, a lower gap layer 71d, a MR layer 71e, an upper gap layer 71f and an upper shield layer 71g on a base board 71a. Pulled-out electrodes and hard layers are not shown in the drawing. The inductive head 72 is constructed by sequentially laminating a gap layer 72b, an upper core layer 72c and an insulation layer 72d on a lower core layer 72a that also serves as the upper shield layer. The portion inserted between the lower shield layer 71c and the upper shield layer 71g serves as a read magnetic gap Gaxe2x80x2 of the MR head 71. The portion inserted between the lower core layer 72a and the upper core layer 72c serves as a write magnetic gap Gbxe2x80x2 of the inductive head 72.
The magnetic head 70 is mounted on a base board 62 by being slanted at an azimuth angle àxxe2x80x2, and the base board 62 on which the magnetic head 70 is mounted is attached at a prescribed position on the outer circumference face of the rotary drum 61.
Likewise, the magnetic head 80 is composed of a MR head 81 having a MR layer 81e and an inductive head 82 as shown in FIG. 29, and has a read magnetic gap Gaxe2x80x3 and a write magnetic gap Gbxe2x80x3. The magnetic head 80 is also mounted on the base board 62 by being slanted at an azimuth angle Ay as shown in FIGS. 24 and 29, and the base board 62 on which the magnetic head 80 is mounted is attached at a prescribed position on the circumference face of the rotary drum 61.
Since the magnetic heads 70 and 80 are alternately used for continuous recording and reproduction in the helical scan type magnetic recording and reproducing apparatus making use of the magnetic heads 70 and 80 comprising the foregoing thin film magnetic head, it is required that the MR layer 71e of the MR head 71 is located at an approximately the same elevation as that of the MR layer 81e of the MR head 81 from the base board 62 as shown in FIG. 29. In other words, the elevation h1 as measured from the base board 62 to the end of the MR layer 71e is approximately equal to the elevation h2 as measured from the base board 62 to the end of the MR layer 81e. The reason will be described below.
When the elevation h1 as measured from the base board 62 to the end of the MR layer 71e is different from the elevation h2 as measured from the base board 62 to the end of the MR layer 81e, the positions of the recording tracks T11 and T12 of the MR heads 71 and 81 turn out to be relatively different from the positions of the reproduction tracks R11 and R12 of the MR heads 71 and 81, respectively, as shown in FIG. 30, thereby causing poor reading. In other words, the position of the reproduction track R12 of the MR head 81 does not come to the center of the recording track T12 when the signal on the recording track T12 is reproduced, even when the position of the reproduction track R11 of the MR heads 71 is adjusted to come at the center of the width of the recording track T11 as shown in FIG. 30. Consequently, the MR head 81 reproduces the recorded signals at the off-center positions of the recording track T12, thereby the reproduction output of the recorded signals on the recording track T12 is reduced to make continuous and proper reproduction to be difficult. Accordingly, the elevations h1 of the MR layer. 71e of the MR head 71 and the elevation h2 of the MR layer 81e of the MR head 81 as measured from the base board 62 should be equal one another in the helical scan type magnetic recording and reproducing apparatus.
As disclosed by the inventors of the present invention in Japanese Patent Application No. 11-83701, however, the MR heads 71 and 81 are manufactured via a step for cutting the base board 71a and 81a with a prescribed angle in the production process for providing azimuth angles àxxe2x80x2 and àxxe2x80x2. Consequently, dimensional errors may be caused in the cutting step to arise positional distributions of the MR layers 71e and 81e. 
Also, mounting errors cannot be ignored since the magnetic heads 70 and 80 may be sometimes mounted on the base board 62 by being shifted toward the direction of elevation h as shown in FIG. 30. As a result, the elevation h1 of the MR layer 71e of the MR head 71 may be different from the elevation h2 of the MR layer 81e of the MR head 81 when measured from the base board 62.
Accordingly, a so-called positioning work of the elevation for adjusting respective end portions of the MR heads to have the same elevation one another is required when these plural magnetic heads are mounted on the base board 62 in the helical scan type magnetic recording and reproducing apparatus, by selecting plural magnetic heads having equal elevations of the MR layers one another in the MR heads.
However, since the MR layers 71e and 81e comprise very thin films, it is difficult to confirm the positions of the MR layers 71e and 81e using, for example, an optical microscope, or it is difficult to select the magnetic heads having the same positions of the MR layers 71e and 81e, or having the same elevations of the end portions of the MR layers 71e and 81e. In addition, the elevation positioning work also takes much time.
Accordingly, it is an object of the present invention, proposed by taking the forgoing situations into consideration, to provide a thin film magnetic head to be used for the helical scan type magnetic recording and reproducing apparatus that is ready for positioning of elevations of the MR layers, besides being most suitable for high density recording that allows proper recording and reproduction.
The present invention completed for solving the foregoing problems provides a thin film magnetic head comprising a lower shield layer made of a magnetic material formed on a substrate, a lower gap layer made of a non-magnetic material formed on the lower shield layer, a magnetoresistive layer formed on the lower shield layer via the lower gap layer, an upper gap layer made of a non-magnetic material formed on the magnetoresistive layer, and an upper shield layer made of a magnetic material formed on the magnetoresistive layer via the upper gap layer, wherein at least either a convex portion or a concave portion is provided on at least one principal face of both principal faces on at least one shield layer of either the upper shield layer or the lower shield layer.
Since either the convex portion or the concave portion is provided on the shield layer in the thin film magnetic head according to the present invention, at least either the convex portion or the concave portion being provided with a prescribed positional relation to the magnetoresistive layer, the convex portion or the concave portion serves as a marker for specifying the magnetoresistive layer. Consequently, the position of the magnetoresistive layer can be specified by detecting this marker. Consequently, it is made possible in the thin film magnetic head according to the present invention to position the mounting elevation of the respective magnetoresistive layers one another based on the position of the marker.
Preferably, a part of at least either the convex portion or the concave portion provided on the shield layer is provided at a position opposed to the magnetoresistive layer.
Preferably, the thin film magnetic head according to the present invention allows data to be read into a magnetic recording medium by a relative movement against the magnetic recording medium, wherein the end portion of at least either the convex portion or the concave portion provided on the shield layer has an approximately the same elevation as the elevation of the end portion of the magnetoresistive layer by taking the travel direction of the magnetic recording medium relative to the magnetoresistive layer as a reference, thereby allowing the position of the magnetoresistive layer to be readily specified.
Preferably, at least either the concave portion or the convex portion provided on the shield layer has an approximately the same width as the longitudinal width on a sliding face of the recording medium of the magnetoresistive layer.
Both of the convex portion and concave portion provided on the shield layer are preferably provided at a position being out of the position opposing to the upper core layer, when the thin film magnetic head comprises a gap layer made of a non-magnetic material formed on the upper shield layer, and an upper core layer made of a magnetic material formed on the upper shield layer via the gap layer, because the presence of the concave portion or the convex portion does not affect the writing gap due to the arrangement of the convex portion and the concave portion.